Comet deflection mission, illustration. This comet is an example of a nearEarth object (NEO), an astronomical object whose orbit intersects with that of the Earth. Comets are bodies of ice and dust that enter the inner solar system from the outer solar system. As they approach the Sun, the heat boils the ice, producing a coma around the nucleus, along with a tail stretching out behind it. Comets passing near the Earth can be a spectacular sight, and have been seen as omens of doom. They are relatively large bodies, and a cometary nucleus can be several kilometres across. Large comets impacting the Earth can cause mass loss of life.Detlev Van RavenswaayScience Photo Library
